The pharmaceutical industry employs various methods for compounding pharmaceutical agents in tablet formulations. In particular, wet granulation is one of the most prevalent methods.
A variety of bisphosphonic acids have been disclosed as being useful in the treatment and prevention of diseases involving bone resorption. Representative examples may be found in the following: U.S. Pat. No. 3,962,432; U.S. Pat. No. 4,054,598; U.S. Pat. No. 4,267,108; U.S. Pat. No. 4,327,039; U.S. Pat. No. 4,621,077; U.S. Pat. No. 4,624,947; U.S. Pat. No. 4,746,654; U.S. Pat. No. 4,922,077; and EPO Patent Pub. No. 0,252,504. Standard methods for tablet formulation of bisphosphonic acids, however, suffer serious difficulties.
In particular, bisphosphonic acids which bear a basic nitrogen-containing functionality may interact with the lactose of standard formulations resulting in discoloration, instability and potency loss. This degradation of the active ingredient is particularly pronounced in the presence of water and/or elevated temperature. It is speculated that this incompatibility is specifically due to the Maillard (or "browning") reaction in which the free amino group of the bisphosphonic acid reacts with the "glycosidic" hydroxyl group of a sugar (such as lactose) ultimately resulting in the formation of brown pigmented degradates. Although this problem may be avoided by the elimination of lactose, the use of lactose as an inert diluent is generally desirable.
The present invention solves this problem by providing a tablet formulation and process therefor that avoids such interaction between the bisphosphonic acid and the lactose in the formulation. In addition, the present invention also provides a processing advantage since it requires only blending of the ingredients without granulation or addition of water prior to compression.